Zeolites are aluminosilicate minerals that are exceedingly useful in a variety of applications, including oil refining, sorption and separation processes, as size-/shape-selective heterogeneous catalysts, as encapsulators, as slow-release agents, and in ion-exchanges, to name a few. However, the pore size of most zeolites (less than 0.74 nanometers in diameter) often limits the use of zeolites in many applications.
In petroleum processes, upgrading or “cracking” hydrocarbons is often used to refine crude oil and other high molecular weight hydrocarbons into much more valuable, smaller “light” hydrocarbons, such as gasoline and olefinic gases. One of the most common upgrading techniques is catalytic cracking, in which catalysts, most commonly conventional zeolite catalysts, are used to upgrade the hydrocarbons. However, due to the small pore size, (<20 Å), high molecular weight hydrocarbons must first undergo distillation and thermal cracking prior to catalytic cracking. Thermal cracking requires significant energy consumption and these additional steps increase the time and cost of the oil refining process.
While mesoporous silicas may provide a larger pore size, eliminating the preconditioning steps, silica-based materials lack the necessary acidity imparted by zeolites and, as such, have reduced catalytic activity. Moreover, attempts to increase acidity by incorporating the heteroatoms found in zeolites (such as aluminum), results in structure destabilization, as a significant percentage of silicon atoms in the framework must be removed.